The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, all color videos are currently input and output in the RGB format. In other words, all colors may be expressed with colors of Red (R), Green (B), and Blue (B). However, the RGB format has such a high correlation between respective color channels that the compression ratio is disadvantageously low when a video is encoded in the RGB format. Accordingly, general commercial applications currently use a video format of YCbCr format, not the RGB format, in carrying out storage, transmission, and compression of a video. A method of converting the RGB format to the YCbCr format is defined in an international standard group, such as the International Telecommunication Union (ITU) or the Society of Motion Picture and Television Engineers (SMPTE). In the YCbCr, Y refers to a luminance component and Cb and Cr refer to chrominance components, and the correlation between respective color channels is substantially removed.
Most commercial applications currently use a signal in the 4:2:0 format, as well as a signal simply converted to the YCbCr format. FIG. 1 is a diagram illustrating the YCbCr 4:4:4 format, FIG. 2 is a diagram illustrating the YCbCr 4:4:2 format, and FIG. 3 is a diagram illustrating the YCbCr 4:2:0 format. According to the YCbCr 4:2:0 format, information on chrominance signals, i.e. Cb and Cr, is transversely and longitudinally sub-sampled by ½, so that the information on the chrominance signals is decreased to ¼ as illustrated in FIG. 3. This uses the fact that a person is more sensitive to a luminescence signal than a chrominance signal. Accordingly, most of the current video codecs including the MPEG-2/4, H.263, and H.264/MPEG-4 AVC basically encode and decode an input video in the YCbCr 4:2:0 format.
However, in this case, the chrominance signal of an encoded image experiences a great loss when compared to an original image. Accordingly, the professional application field, such as a digital cinema, a medical image, and an Ultra High Definition Television (UHDTV), uses the RGB 4:4:4 format or the YCbCr 4:4:4 format, not the YCbCr 4:2:0 format.
In order to support the format, the H.264/AVC AMD supports a signal processing in an RGB area with high 4:4:4 intra/predictive profiles, and includes two supportive methods. The first method is a common mode method of commonly applying an intra/inter mode which has been determined at the time of encoding a green chrominance signal, to the encoding of a blue chrominance signal and a red chrominance signal in the processing of an RGB signal. The second method is an independent mode method of independently processing each of R, G, and B signals. However, in this case, the compression ratio of an encoded image is deteriorated due to the high correlation between the R, G, and B signals as described above.
Accordingly, the high correlation between chrominance signals fundamentally exists in the RGB area, so that a research for improving the efficiency of an encoder through the removal of the correlation has been conducted.    [Document 1] Byung Cheol Song, Yun Gu Lee, and Nak Hoon Kim “Block Adaptive Inter-Color Compensation Algorithm for RGB 4:4:4 Video Coding,” IEEE CYST., vol. 18, no. 10, pp. 1447-1451, October, 2008.    [Document 2] Y.-H. Kim, S.-Y. Jung, B. H. Choi and J. K. Park, “High Fidelity RGB Video coding Using Adaptive Inter-Plane Weighted Prediction,” IEEE CVST., vol. 19, No. 7, pp 1051˜1056, July, 2009.
In Document 1, understanding the fact that the linear relation is represented between R, G, and B signals served as an insight in the improvement of the encoding efficiency by initially encoding a G plane as illustrated in FIG. 4 and then encoding R and B planes by using information on an encoded G plane. As can be seen in FIG. 5, in Document 2, likewise to Document 1, a G plane is first encoded, a B plane to be encoded next is processed with the use of a previously encoded G plane, and an R plane is finally encoded using a previously encoded B plane, as well as the previously encoded G plane. That is, in the event of encoding the R plane, since not only the G plane but also the B plane are already encoded, the R plane is encoded by selecting the plane having the higher encoding efficiency in the two planes. In this case, the higher encoding efficiency may be achieved in Document 2 compared to the encoding of the R plane by using only the G plane in Document 1.
However, according to the aforementioned existing technology, a predicted image is generated using information on only one plane when a predicted image between planes is generated, so that the prediction efficiency is disadvantageously deteriorated.